It is known that aqueous dispersions of polymers of olefinically unsaturated monomers can be prepared in the presence of water-soluble or water-dispersible oligourethanes of anionic or cationic character (DE-A-1 953 349).
However, it has been found that, in general, the oligourethanes described therein are not entirely suitable for the emulsification of hydrophobic monomers and the resulting polymers. To obtain stable dispersions without any significant loss of polymer and without sedimentation, a low molecular weight emulsifier also has to be added in many cases. The reason for the poor emulsification behavior of these oligourethanes lies in their structure. This is because the oligourethanes used as emulsifiers in DE-A-1 953 349 are compounds having a linear molecular structure which have been prepared using predominantly difunctional (potentially) ionic synthesis components and in which therefore the hydrophilic ionic centers are incorporated within the chain.